In radar systems, an electromagnetic signal typically having a pulsed waveform is transmitted from a radar antenna, reflected from a target or targets, and received at a radar receiver. The range resolution of the radar system improves with increasing bandwidth of the electromagnetic signal transmitted by the radar. Because typical radar systems may operate at frequencies which include reserved or restricted frequency bands, high-bandwidth electromagnetic signal transmittal may interfere with communications, navigation, or other uses of these frequency bands. In particular, if other systems operate in relatively narrow frequency bands, the wide-band spectrum of the transmitted electromagnetic signal waveform should have notches or stop-bands at the respective frequency bands, with widths in proportion to the bandwidths of the respective frequency bands.
Additional desirable properties for waveforms of high-bandwidth transmit electromagnetic signals include a constant or near-constant modulus, to accommodate physical constraints in peak power for radar transmitters; and good pulse compression properties, for target discrimination. For example, due to its performance under each of these criteria, the ‘chirp’ or linear frequency modulated (LFM) electromagnetic signal is widely used in known radar systems. However, because of its near-constant power spectral density over its bandwidth, the chirp electromagnetic signal may cause interference with other systems that are in the radar's operational range and operating at frequency bands within the radar's transmit signal waveform bandwidth. Thus, various methods have been developed for modifying the waveform of the electromagnetic transmit signal to have minimal power spectral density over these frequency bands.